1. Field of the Invention
The present invention relates to an electric power steering apparatus equipped with an electric motor for generating assist torque to the steering wheel of a vehicle, and a control unit for controlling the driving of the electric motor.
2. Description of the Related Art
In the past, such an electric power steering apparatus equipped with a electric motor for generating assist torque to the steering wheel of a vehicle and a control unit for controlling the driving of the electric motor has been known, in which the control unit can be assembled separately from the electric motor and is mounted onto the electric motor in its assembled state through a bracket (for example, see a first patent document: Japanese patent application laid-open No. 2002-127921).
In this electric power steering control apparatus, the control unit has a power board on which is mounted a bridge circuit comprising a plurality of semiconductor switching elements for switching an electric current supplied to the electric motor in accordance with the torque assisting the driver's operation of the steering wheel, and a heat sink is stacked or mounted on the power board so as to dissipate the heat generated due to the operations of the semiconductor switching elements.
In the above-mentioned electric power steering control apparatus, however, there arises the following problem. That is, the heat sink, which is stacked or mounted on the power board so as to dissipate the heat generated due to the operations of the semiconductor switching elements, is of a planar configuration, so it has a limited heat dissipation area and is poor in its heat dissipation capability.